For cultivating cells, in the past, a culture medium was supplemented with serum, which serves as a universal nutrient for the growth and maintenance of all mammalian cell lines that produce biologically active products. Although widely used, the serum has many limitations. It contains high levels of numerous proteins which interfere with the limited quantities of the desired protein of interest produced by the cells. The proteins derived from the serum must be separated from the product during downstream processing such as purification of the protein of interest, which complicates the process and increases the cost. Further, when culturing cells with the serum, a risk of causing infections exists, and the quality between batches is difficult to control. There is therefore a great demand for the development of alternative media free from animal serum for maintaining the growth of cells during the production of biologically active products.
A cell attachment factor (such as an extracellular matrix (ECM)) is used to coat on a substrate for cell culture for promoting the growth of cells, when the cells are cultivated with a serum-free medium. On the other hand, cells cultivated without the extracellular matrix are induced to undergo apoptosis. Generally, an extracellular matrix can include a glycosaminoglycan (GAG) or further include a fibrous protein (such as collagen, laminin, fibronectin, or elastin). For example, the serum-free medium StemPro MSC SFM (sold and manufactured by Invitrogen) has to be used with a petri dish coated with the extracellular matrix for cell culture. However, since the principal component of an extracellular matrix is protein which is generally obtained from organisms, the extracellular matrix has a high cost. Further, the quality of an extracellular matrix prepared and purified from human tissue or blood is unstable.
For the foregoing reasons, there is a need for new methods for promoting the growth of cells, especially when cultivated under serum-free and extracellular-matrix free conditions.